Detection apparatus, power supply system, and method of controlling detection apparatus

ABSTRACT

A detection apparatus includes: a measurement coil disposed in a vicinity of a power reception coil configured to receive power supplied through a magnetic field; a measurement section configured to measure a voltage of the measurement coil as a measurement coil voltage; and a foreign object detection section configured to obtain an electrical characteristic value of at least one of the power reception coil and the measurement coil on the basis of the measurement coil voltage, and to detect a foreign object in the magnetic field if the electrical characteristic value is lower than a predetermined lower limit threshold value.

CROSS REFERENCE TO RELATED APPLICATION

This present application is a Continuation of application Ser. No.14/259,358, filed Apr. 23, 2014, which claims priority to JapanesePriority Patent Application JP 2013-103629 filed May 16, 2013, theentire contents of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to a detection apparatus, a power supplysystem, and a method of controlling a detection apparatus. Morespecifically, the present disclosure relates to a detection apparatusthat detects a foreign object in a magnetic field, a power supplysystem, and a method of controlling a detection apparatus.

In recent years, public attention has been drawn to power supply systemsin which power is supplied to CE (Consumer Electronics) devices, such asa mobile phone, a mobile music player, and the like in an electricallynon-contact manner. These power supply systems are referred to asnon-contact power supply systems, non-contact power transmissionsystems, wireless power supply systems, or the like. With these systems,it is possible to charge secondary devices by a simple method, forexample placing a secondary device, such as an electronic device, or thelike on a primary device, such as a power supply device, or the like.That is to say, a terminal connection becomes unnecessary between anelectronic device and a power supply device.

As a method of performing non-contact power supply in this manner, anelectromagnetic induction method has been familiar. Also, recently, anon-contact power supply system using a method called a magnetic fieldresonance method (or a magnetic resonance method) with the use ofresonance phenomena has attracted attention.

A non-contact power supply system using the magnetic field resonancemethod has an advantage in that it is possible to perform powertransmission on a principle of resonance phenomena between devices thatare disposed more apart from each other than in the case of theelectromagnetic induction method. Also, the non-contact power supplysystem using the magnetic field resonance method has an advantage inthat even if axis alignment between a power supply coil of a powersupply source and a power reception coil of a power supply destinationis deteriorated in some degree, power transmission efficiency (that isto say, power supply efficiency) is not decreased so much.

However, both of the magnetic field resonance method and theelectromagnetic induction method are non-contact power supply systemsusing magnetic coupling between the power supply coil of the powersupply source and the power reception coil of the power supplydestination.

Incidentally, one of important elements of a non-contact power supplysystem is a countermeasure against heat generation by a foreign object,such as metal, a magnetic body, a magnet, and the like that mightgenerate heat through lines of magnetic force. In a non-contact powersupply system using an electromagnetic induction method or a magneticfield resonance method, if a foreign object is put into a gap between apower supply coil and a power reception coil, the foreign object mightgenerate heat by lines of magnetic force passing through the foreignobject. This heat generation of the foreign object is caused by an eddycurrent loss generated in a metallic foreign object by the passage oflines of magnetic force through the metallic foreign object, ahysteresis loss generated in a foreign magnetic body, and the like bythe passage of lines of magnetic force through a foreign magnetic body,a foreign magnet, or the like.

Heat generation by a foreign object might cause malfunction or damage ofa power supply device and an electronic device, and the like.Accordingly, the prevention of heat generation by a foreign object issaid to be a major task for a non-contact power supply system.

As a countermeasure against the heat generation, a method of adding atemperature sensor in order to detect heat generation by a foreignobject is provided. However, in this method, a foreign object that hasalready generated heat is to be detected, and thus this method isdifficult to become a fundamental countermeasure against heat generationby a foreign object. That is to say, it is desirable to provide a methodof detecting a foreign object that might generate heat through lines ofmagnetic force before the foreign object actually generates much heat.

Thus, a proposal has been made of a method of checking changes inelectrical parameters (a current, a voltage, and the like) when there isa metallic foreign object inserted between a power supply apparatus anda power reception apparatus, and determining the presence or absence ofthe metallic foreign object. By such a method, it is possible to detectexistence of a foreign object before the foreign object generates muchheat. Specifically, a proposal has been made of a method of detecting ametallic foreign object by changes in amplitude and phase at the time ofcommunication between the power supply apparatus and the power receptionapparatus (for example, refer to Japanese Unexamined Patent ApplicationPublication No. 2008-206231). Also, a proposal has been made of a methodof detecting a metallic foreign object by an eddy current loss (forexample, refer to Japanese Unexamined Patent Application Publication No.2001-275280).

SUMMARY

However, in the related-art technique described above, it is difficultto correctly detect a foreign object. In the above-described systems, noconsideration has been given to the influence on a metallic housing of apower reception apparatus. In the case of charging a common electronicdevice, it is highly possible that a metal of some kind (a metallichousing, a metallic part, or the like) is used for an electronic device.Accordingly, it is difficult to determine whether a change in aparameter is caused by “influence by a metallic housing, or the like”,or by “unexpected existence of a metallic foreign object”. For example,in the case of detecting a foreign object by a change of an eddy currentloss, it is difficult to determine whether an eddy current loss isgenerated by a metallic housing of an electronic device, or by theunexpected existence of a metallic foreign object between a power supplyapparatus and a power reception apparatus. This is the same for the caseof detecting a foreign object by a change in amplitude and phase.

The present technique has been made in view of these circumstances, andit is desirable to correctly detect a foreign object in a magneticfield.

The present technique has been made in order to address theabove-described problems. According to an embodiment of the presentdisclosure, there is provided a detection apparatus including: ameasurement coil disposed in a vicinity of a power reception coilconfigured to receive power supplied through a magnetic field; ameasurement section configured to measure a voltage of the measurementcoil as a measurement coil voltage; and a foreign object detectionsection configured to obtain an electrical characteristic value of atleast one of the power reception coil and the measurement coil on thebasis of the measurement coil voltage, and to detect a foreign object inthe magnetic field if the electrical characteristic value is lower thana predetermined lower limit threshold value, and a method of controllingthe detection apparatus. Thereby, if the electrical characteristic valueis lower than a predetermined lower limit value, the working effect ofdetection of a foreign object is brought about.

Also, in the above-described embodiment, if the electricalcharacteristic value is lower than the lower limit threshold value, orif the electrical characteristic value is higher than an upper limitthreshold value greater than the lower limit threshold value, theforeign object detection section may be configured to detect the foreignobject. Thereby, if the electrical characteristic value is lower thanthe lower limit threshold value, or if the electrical characteristicvalue is higher than an upper limit threshold value greater than thelower limit threshold value, the working effect of detection of aforeign object is brought about.

Also, in the above-described embodiment, the upper limit threshold valuemay be higher than a reference value being the electrical characteristicvalue when there is no foreign object, and the lower limit thresholdvalue may be a lower value than the reference value. Thereby, if theelectrical characteristic value is lower than a lower limit value lessthan the reference value, the working effect of detection of a foreignobject is brought about.

Also, in the above-described embodiment, the measurement section may beconfigured to further measure a voltage and a current of the powerreception coil, and the foreign object detection section may beconfigured to obtain impedance of the power reception coil from themeasurement coil voltage, and the voltage and the current of the powerreception coil as the electrical characteristic value. Thereby, theworking effect of obtaining impedance of the power reception coil as theelectrical characteristic value is brought about.

Also, in the above-described embodiment, the measurement section may beconfigured to further measure a voltage of the power reception coil as apower reception coil voltage, and the foreign object detection sectionmay be configured to obtain a voltage ratio of the measurement coilvoltage and the power reception coil voltage as the electricalcharacteristic value. Thereby, the working effect of obtaining thevoltage ratio as the electrical characteristic value is brought about.

Also, in the above-described embodiment, the measurement section may beconfigured to further measure a voltage of the power reception coil as apower reception coil voltage, the power reception coil may be configuredto receive first and second power having a different amount of powerwith each other in sequence, and the foreign object detection sectionmay be configured to obtain, as the electrical characteristic, adifference between the voltage ratio obtained when the first power isreceived, and the voltage ratio obtained when the second power isreceived. Thereby, the working effect of obtaining the differencebetween the voltage ratios as the electrical characteristic value isbrought about.

Also, in the above-described embodiment, the measurement coil may beconfigured to have a smaller coil surface area than that of the powerreception coil. Thereby, the working effect of measuring the voltage ofthe measurement coil smaller than that of the power reception coil isbrought about.

Also, in the above-described embodiment, the measurement coil may bedisposed inside the power reception coil. Thereby, the working effect ofmeasuring the voltage of the measurement coil disposed inside the powerreception coil is brought about.

Also, in the above-described embodiment, the measurement coil may bedisposed on a substantially same plane as that of the power receptioncoil. Thereby, the working effect of measuring the voltage of themeasurement coil disposed on a substantially same plane as that of thepower reception coil is brought about.

Also, in the above-described embodiment, the measurement coil may bedisposed at a position where a coil surface of the measurement coil andthat of the power reception coil have a substantially same centerposition. Thereby, the working effect of measuring the voltage of themeasurement coil disposed at a position where a coil surface of themeasurement coil and that of the power reception coil have asubstantially same center position is brought about.

Also, in the above-described embodiment, the power may be power suppliedfrom a power supply apparatus, and the detection apparatus may furtherinclude a transmission section configured to transmit a control signalrequesting a decrease in an amount of the power if the foreign object isdetected. Thereby, the working effect of transmitting a control signalrequesting a decrease in the amount of the power if the foreign objectis detected is brought about.

According to another embodiment of the present disclosure, there isprovided a detection apparatus including: a measurement coil disposed ina vicinity of a power supply coil configured to supply power through amagnetic field; a measurement section configured to measure a voltage ofthe measurement coil as a measurement coil voltage; and a foreign objectdetection section configured to obtain an electrical characteristicvalue of at least one of the power reception coil and the measurementcoil on the basis of the measurement coil voltage, and to detect aforeign object in the magnetic field if the electrical characteristicvalue is lower than a predetermined lower limit threshold value.Thereby, if the electrical characteristic value is lower than apredetermined lower limit value, the working effect of detection of aforeign object is brought about.

According to another embodiment of the present disclosure, there isprovided a power supply system including: a power supply coil configuredto supply power through a magnetic field; a power reception coilconfigured to receive the power; a measurement coil disposed in avicinity of the power reception coil; a measurement section configuredto measure a voltage of the measurement coil as a measurement coilvoltage; and a foreign object detection section configured to obtain anelectrical characteristic value of at least one of the power receptioncoil and the measurement coil on the basis of the measurement coilvoltage, and to detect a foreign object in the magnetic field if theelectrical characteristic value is lower than a predetermined lowerlimit threshold value. Thereby, the working effect of detection of aforeign object on the basis of the measurement coil voltage is broughtabout.

By the present technique, it is possible to obtain an advantage ofcorrectly detecting a foreign object in a magnetic field.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating an example of a configurationof a non-contact power supply system according to a first embodiment;

FIG. 2 is a block diagram illustrating an example of a configuration ofa power supply apparatus according to the first embodiment;

FIG. 3 is a block diagram illustrating an example of a configuration ofa power reception apparatus according to the first embodiment;

FIGS. 4A and 4B are diagrams illustrating an example of a powerreception coil and a detection coil according to the first embodiment;

FIG. 5 is a block diagram illustrating an example of a configuration ofa foreign object detection section according to the first embodiment;

FIG. 6 is a flowchart illustrating an example of operation of the powersupply apparatus according to the first embodiment;

FIG. 7 is a flowchart illustrating an example of operation of the powerreception apparatus according to the first embodiment;

FIG. 8 is a graph illustrating an example of a temperature change of aforeign object according to the first embodiment;

FIG. 9 is a graph illustrating an example of an impedance change of thepower reception coil according to the first embodiment;

FIG. 10 is a graph illustrating an example of a change in AK accordingto a second embodiment;

FIG. 11 is a graph illustrating an example of a change in voltage ratioaccording to a third embodiment;

FIG. 12 is a graph illustrating an example of a voltage change of adetection coil according to a fourth embodiment;

FIGS. 13A to 13G are sectional views illustrating examples ofdisposition of a power reception coil and a detection coil according tovariations, respectively;

FIG. 14 is a block diagram illustrating an example of a foreign objectdetection apparatus disposed inside of a power supply apparatusaccording to the first embodiment;

FIG. 15 is a block diagram illustrating an example of a foreign objectdetection apparatus disposed outside of a power supply apparatusaccording to the first embodiment; and

FIG. 16 is a block diagram illustrating an example of a first foreignobject detection apparatus disposed inside of a power supply apparatusand a second foreign object detection apparatus disposed inside of apower reception apparatus according to the first embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following, descriptions will be given of modes for carrying outthe present technique (hereinafter referred to as embodiments). Thedescriptions will be given in the following order.

1. First embodiment (example of detecting a foreign object on the basisof impedance)

2. Second embodiment (example of detecting a foreign object on the basisof AK)

3. Third embodiment (example of detecting a foreign object on the basisof voltage ratio)

4. Fourth embodiment (example of detecting a foreign object on the basisof detection coil voltage)

5. Variations

1. First Embodiment Example of Configuration of Non-Contact Power SupplySystem

FIG. 1 is a perspective view illustrating an example of a configurationof a non-contact power supply system according to a first embodiment.The non-contact power supply system is a system for supplying power inan electrically non-contact manner through a magnetic field. Thenon-contact power supply system includes a power supply apparatus 100,and power reception apparatuses 400 and 401. In this regard, the numberof the power reception apparatuses is not limited to two, and may beone, three or more.

The power supply apparatus 100 supplies power to the power receptionapparatuses 400 and 401 in an electrically non-contact manner. Bynon-contact power supply, a user is allowed to charge the powerreception apparatuses 400 and 401 by easy operation, such as placing thepower reception apparatuses 400 and 401 on the power supply apparatus100, or the like without making a terminal connection to an AC(Alternating Current) adapter, or the like. Such a charging methodreduces workload of the user.

The power supply apparatus 100 is formed in a planar shape having acertain area, for example. Specifically, the power supply apparatus 100is formed in the shape of a shallow box (a so-called tray state), in theshape of a mat (a so-called mat state), or in a shape having a slightheight with a flat upper part (a so-called table state). The lower partor the surface of the plane (hereinafter, referred to as a “power supplyface”.) is provided with a power supply coil that generates a magneticfield.

It is desirable that the surface of the power supply face issufficiently larger than the areas of the power reception faces of thepower reception apparatuses so that a plurality of the power receptionapparatuses, such as the power reception apparatuses 400 and 401, andthe like are allowed to be placed on the surface. Here, the powerreception face is a plane including a lower part or a surface on which apower reception coil that receives power supplied through a magneticfield is disposed. By placing a plurality of power reception apparatuseson the power supply face, it is possible for the non-contact powersupply system to charge these apparatuses at the same time or insequence.

In this regard, a configuration in which the area of the power supplyface is larger than the area of the power reception face is employed.However, the configuration is not limited to this configuration. Theareas may be nearly equal, or the area of the power supply face may besmaller than that of the power reception face. Also, it is possible tocharge the power reception apparatus 400, and the like only by beingbrought close, and thus the shape of the power supply apparatus 100 isnot limited to a shape having a plane. For example, the power supplyapparatus 100 may be desk-top shape, such as a desk holder, a cradle,and the like.

Also, the power supply apparatus 100 has a configuration for onlycharging. However, together with charging, the power supply apparatus100 may perform bi-directional data transfer with the power receptionapparatus 400.

The power reception apparatus 400 receives power supplied from the powersupply apparatus 100 through a magnetic field. For example, electronicdevices, such as a mobile telephone terminal, an electronic stillcamera, and the like are used as the power reception apparatus 400. Thepower reception apparatus 400 detects the presence or absence of aforeign object in a magnetic field. And if a foreign object is detected,the power reception apparatus 400 requests the power supply apparatus100 to decrease the amount of power supply. The power supply apparatus100 decreases the amount of power supply in response to the request.Thereby, heat generation of the foreign object is prevented. The powerreception apparatus 401 has the same configuration as that of the powerreception apparatus 400.

In this regard, the power reception apparatus 400 may be equipment otherthan an electronic device, such as an electric vehicle, and the like. Inthe case of an electric vehicle, the power reception apparatus 400 isallowed to detect a metallic foreign object attached to the vehicle bodytogether with mud, and so on, for example.

Example of Configuration of Power Supply Apparatus

FIG. 2 is a block diagram illustrating an example of a configuration ofthe power supply apparatus 100 according to the first embodiment. Thepower supply apparatus 100 includes a power conversion circuit 110, apower supply control section 120, a demodulation circuit 130, animpedance matching circuit 140, a capacitor 150, and a power supply coil160.

The power conversion circuit 110 is a circuit that converts the voltageand the frequency of the power supplied from an external power supplysource of the power supply apparatus 100, and generates AC power forperforming power transmission. Also, when the power supply controlsection 120 instructs to change the frequency, the power conversioncircuit 110 changes the frequency of the generated AC power. Here, theexternal power supply source is a commercial power source to be suppliedthrough a plug socket (a so-called outlet), for example.

The power supply control section 120 controls the amount of powersupplied to the power reception apparatus 400. When the power source ofthe power supply apparatus 100 is turned on, the power supply controlsection 120 controls the power conversion circuit 110 to start supplyinga predetermined amount of power W1 to the power reception apparatus 400.Here, the amount of power W1 is set to a minimum amount of power thatallows the power reception apparatus 400 to operate, for example.

And the power supply control section 120 receives a power supply controlsignal for controlling the amount of power supply from the powerreception apparatus 400 through the demodulation circuit 130. The powersupply control section 120 controls the amount of power supply inaccordance with the power supply control signal. The power supplycontrol signal includes a signal for requesting an increase in theamount of power supply and a signal for requesting a decrease in theamount of power supply, for example.

If an increase in the amount of power supply is requested, the powersupply control section 120 controls the power conversion circuit 110 tocause the power reception apparatus 400 to supply the amount of power W2that is higher than the amount of power W1. Here, the amount of power W2is set to the amount of power that is sufficient for the power receptionapparatus 400 to charge a secondary battery, and the like.

And when the amount of power is W2, if a decrease in the amount of powersupply is requested, the power supply control section 120 controls thepower conversion circuit 110 to return the amount of power to W1. Inthis regard, the power supply control section 120 controls the amount ofpower in the two stages W1 and W2. However, the power supply controlsection 120 may perform three-stage control, or may control the startand the stop of power supply.

The control of the amount of power supply is performed by the powersupply control section 120 exerting control on the power conversioncircuit 110 so as to change the AC frequency, for example. Specifically,if the power supply control section 120 increases the amount of powersupply, the power supply control section 120 matches the AC frequencywith a specific frequency (for example, a resonance frequency). If thepower supply control section 120 decreases the amount of power supply,the power supply control section 120 performs control so that the ACfrequency becomes a different value from the specific frequency.

In this regard, the control of the amount of power supply is not limitedto changing the AC frequency. For example, the power supply controlsection 120 may cause the power conversion circuit 110 to increase ordecrease the AC voltage so as to control the amount of power supply.Also, in the case of a configuration in which the power conversioncircuit 110 generates a pulse signal by a switching power source, or thelike to supply the pulse signal to the power supply coil 160, the powersupply control section 120 may control the amount of power supply bychanging the duty ratio of the pulse signal.

The demodulation circuit 130 demodulates an AC signal from the powerreception apparatus 400, and extracts a power supply control signalsuperposed on the AC signal. The demodulation circuit 130 supplies thepower supply control signal to the power supply control section 120.

The impedance matching circuit 140 is a circuit that controls theimpedance of the power-supply side circuit to obtain impedance matchingwith the impedance of the power-reception side circuit. By carrying outimpedance matching, the power transmission efficiency is improved. Inthis regard, if the transmission efficiency is sufficiently high, or thetransmission efficiency is sufficiently improved only by the impedancematching at the power reception side, and the like, a configuration ofnot disposing the impedance matching circuit 140 may be employed.

The capacitor 150 is an element that stores or discharges electricenergy. The capacitor 150 is connected to the power supply coil 160 inseries, for example, and constitutes an LC resonance circuit togetherwith the power supply coil 160. The capacitance value of the capacitor150 is set such that the resonance frequency f1 of the LC resonancecircuit substantially matches the resonance frequency f2 of the LCresonance circuit of the power reception side, or becomes a frequency inthe vicinity of the resonance frequency f2.

In this regard, if the resonance frequency f1 is obtained by a linecapacitance of the power supply coil 160, or a parasitic capacitancecomponent formed by the capacitance between the power supply coil 160and the power reception coil described later, and the like, thecapacitor 150 may not be disposed. Also, in the case where the powertransmission efficiency is sufficiently high, or the like, the capacitor150 may not be disposed.

Also, the capacitor 150 may be a variable capacitor. In that case, thepower supply control section 120 controls the capacitance in order toadjust the resonance frequency.

When AC power is supplied from the power conversion circuit 110, thepower supply coil 160 generates an electromagnetic wave in accordancewith the Ampere's law. Electric power is supplied to the power receptionapparatus 400 through this electromagnetic wave.

In this regard, the power supply apparatus 100 has a configurationincluding only one power supply coil 160. However, the power supplyapparatus 100 may have a configuration including a plurality of powersupply coils 160.

Example of Configuration of Power Reception Apparatus

FIG. 3 is a block diagram illustrating an example of a configuration ofthe power reception apparatus 400 according to the first embodiment. Thepower reception apparatus 400 includes a detection coil 410, a capacitor420, a power reception coil 430, capacitors 440 and 441, and a powerreception control section 450. Also, the power reception apparatus 400includes a charge control section 480, a secondary battery 481, and aload circuit 482.

The detection coil 410 is a coil disposed in the vicinity of the powerreception coil 430, and is used for measuring a voltage in order todetect a foreign object. In this regard, the detection coil 410 is anexample of a measurement coil described in the claims.

The capacitor 420 is an element that stores or discharges electricenergy. The capacitor 420 is connected to the detection coil 410 inseries, for example. The capacitor 420 is used for a resonance purpose,a filter purpose, a coupling purpose, and the like. In particular, inthe case of a resonance purpose, the capacitor 420 constitutes an LCresonance circuit together with the detection coil 410. And thecapacitance value of the capacitor 420 is set such that the LC resonancecircuit has a resonance frequency of f3. Also, in the case of reducingelectromagnetic interference caused by the power supply side, it isdesirable to set the resonance frequency f3 not to match the resonancefrequency f1 of the power supply side. On the contrary, in the case ofpositively using electromagnetic interference caused by the power supplyside, the resonance frequency f3 is sometimes set to match the resonancefrequency f1 of the power supply side. Of course, in situations where aresonance purpose, a filter purpose, a coupling purpose, and the likeare not necessary, it is not necessary to dispose the capacitor 420.

The power reception coil 430 receives power supplied from the powersupply apparatus 100. Specifically, when an electromagnetic wave issupplied from the power supply apparatus 100, the power reception coil430 generates an induction voltage in response to a change in themagnetic flux of the electromagnetic wave in accordance with the law ofelectromagnetic induction.

In this regard, the power reception apparatus 400 has a configurationincluding only one power reception coil 430. However, the powerreception coil 430 may have a configuration including a plurality ofpower reception coils 430. Also, in the case where the power receptioncoil 430 includes a plurality of power reception coils 430, thedetection coil 410 is disposed in the vicinity of at least one of thepower reception coils 430.

The capacitors 440 and 441 are elements that store or discharge electricenergy. The capacitor 440 is connected to the power reception coil 430in series, and the capacitor 441 is connected in parallel with the powerreception coil 430. The capacitors 440 and 441 constitute an LCresonance circuit together with the power reception coil 430. Thecapacitance values of the capacitor 440, and so on are set such that theresonance frequency f2 of the LC resonance circuit substantially matchesthe resonance frequency f1 of the power supply side, or becomes afrequency in the vicinity of the resonance frequency f1.

In this regard, at least one of the capacitors 420 and 440 may be avariable capacitor. In that case, the power reception control section450 controls the capacitance of the variable capacitor in order toadjust the resonance frequency. On the other hand, if the resonancefrequency f2 is obtained by a line capacitance of the power receptioncoil 430, or a parasitic capacitance component formed by the capacitancebetween the power supply coil 160 and the power reception coil 430, andso on, the capacitor 420 and the capacitor 440 may not be disposed.Also, in the case where power transmission efficiency is sufficientlyhigh, or the like, the capacitor 420 and the capacitor 440 may not bedisposed.

Also, the power reception apparatus 400 may further include a resonancecircuit in addition to the resonance circuit including the detectioncoil 410, and the resonance circuit including the power reception coil430.

The power reception control section 450 performs overall control of thepower reception apparatus 400. The power reception control section 450includes a measurement section 451, a foreign object detection section460, a modulation circuit 452, a power reception control circuit 453, animpedance matching circuit 454, a rectification circuit 455, a voltagestabilization circuit 456, and a load connection circuit 457.

Also, the power reception control section 450 includes terminals 471,472, 473 and 474. One end of the detection coil 410 is connected to theterminal 471 through the capacitor 420. The LC resonance circuitincluding the power reception coil 430 is connected to terminals 472 and473. The charge control section 480 is connected to the terminal 474.

The measurement section 451 measures a voltage V₂ and a current I₂ ofthe power reception coil 430, and a voltage V₃ of the detection coil410. The voltage is measured by a voltage transformer, and so on. Ashunt resistor is connected to the power reception coil in series, andthe current is obtained from the potential difference of the both ends,for example. In the measuring, volt (V) is used as a unit of voltage,for example, and ampere (A) is used as a unit of current, for example.

In this regard, the current may be obtained by a current transformer.Also, the measurement section 451 may include an amplification circuitthat amplifies the AC signal, and the voltage amplified by theamplification circuit, and so on may be measured. By the amplificationof the AC signal, it is possible for the measurement section 451 tomeasure the voltage, and the like with high precision.

Hereinafter the voltage V₂ of the power reception coil 430 is referredto as a “power reception coil voltage”, and hereinafter, the current I₂of the power reception coil 430 is referred to as a “power receptioncoil current”. Also, hereinafter the voltage V₃ of the detection coil isreferred to as a “detection coil voltage”. The measurement section 451supplies the measurement values to the foreign object detection section460.

Here, it is assumed that the power reception coil voltage and the powerreception coil current that are to be measured are the voltage and thecurrent before having been rectified by the rectification circuit 455.In this regard, a configuration in which the measurement section 451measures the reception power coil voltage and the power reception coilcurrent after the rectification may be employed.

The foreign object detection section 460 detects a foreign object in amagnetic field from the power supply apparatus 100 on the basis of themeasurement value measured by the measurement section 451. The foreignobject detection section 460 determines whether a load is connected ornot on the basis of the connection control signal from the powerreception control section 450. And the foreign object detection section460 obtains measurement values of when a load is connected and when aload is not connected, and detects a foreign object on the basis of themeasurement values. A detailed description will be given of thedetection method later. The foreign object detection section 460supplies a detection result of a foreign object to the power receptioncontrol section 450.

In this regard, an apparatus including a detection coil 410, ameasurement section 451, and a foreign object detection section 460 isan example of a foreign object detection apparatus described in theclaims. Also, a configuration of including the foreign object detectionapparatus in the power reception apparatus 400 is employed. However, aconfiguration of disposing the foreign object detection apparatusoutside the power reception apparatus 400 may be employed.

The modulation circuit 452 modulates the amplitude of the AC signal, andso on to the power supply apparatus 100 so as to superimpose the powersupply control signal. When the modulation circuit 452 receives thepower supply control signal from the power reception control circuit453, the modulation circuit 452 superimposes the power supply controlsignal on the AC signal. Thereby, the power supply control signal istransmitted to the power supply apparatus 100.

In this regard, the modulation circuit 452 performs load modulation, butmay perform modulation by a modulation method other than the loadmodulation. Also, the power reception apparatus 400 transmits the powersupply control signal by load modulation, but may perform transmissionby the other methods. For example, the power reception apparatus 400 mayfurther include a communication coil, and an antenna, and may transmitthe power supply control signal using the communication coil, and theantenna.

The power reception control circuit 453 controls the amount of powersupply on the basis of a foreign object detection result. When anelectric power of W1 is supplied from the power supply apparatus 100,the power reception control circuit 453 supplies a connection controlsignal instructing disconnection of a load to the load connectioncircuit 457.

And when receiving a measurement termination notification from theforeign object detection section 460, the power reception controlcircuit 453 supplies a connection control signal instructing connectionof a load to the load connection circuit 457, and supplies a powersupply control signal requesting an increase in the amount of powersupply to the modulation circuit 452. Thereby, the amount of powersupply is increased from W1 to W2.

After an electric power of W2 is supplied, when a detection resultindicating detection of a foreign object is received, the powerreception control circuit 453 supplies a connection control signalinstructing disconnection of a load to the load connection circuit 457,and supplies the power supply control signal requesting a decrease inthe amount of power supply to the modulation circuit 452. Thereby, theamount of power supply is decreased from W2 to W1, and thus heatgeneration of a foreign object is restrained.

In this regard, the power reception control circuit 453 requests toreturn the amount of power supply to the initial W1 at foreign objectdetection time. However, the power reception control circuit 453 mayrequest to decrease the amount of power supply to lower than W1 atforeign object detection time. Also, the power reception control circuit453 may request the amount of power supply that is lower than W2, buthigher than W1 at foreign object detection time. Alternatively, thepower reception control circuit 453 may requests to stop power supply atforeign object detection time. Or, the power reception control circuit453 may instruct only disconnection of a load at foreign objectdetection time, and does not request to decrease the amount of powersupply. In the case of not requesting to decrease the amount of powersupply, it is not necessary to dispose the modulation circuit 452. Also,the power reception control circuit 453 disconnects a load at foreignobject detection time. However, the power reception control circuit 453may request to decrease the amount of power supply while connecting aload at foreign object detection time.

Also, the power reception control circuit 453 transmits only the powersupply control signal. However, the power reception control circuit 453may further transmit a detection result of a foreign object separatelyfrom the power supply control signal. In this case, the power supplyapparatus 100 ought to decrease the amount of power supply at foreignobject detection time.

Also, the power reception control circuit 453 controls the rectificationcircuit 455 and the voltage stabilization circuit 456. For example, whenthe amount of power W2 is supplied, the power reception control circuit453 operates the rectification circuit 455 and the voltage stabilizationcircuit 456. And if a foreign object is detected, the power receptioncontrol circuit 453 stops the rectification circuit 455 and the voltagestabilization circuit 456.

The impedance matching circuit 454 is a circuit that controls theimpedance of the power reception circuit to obtain impedance matching ofthe power-supply side circuit. By obtaining impedance matching, thepower transmission efficiency is improved. In this regard, in the casewhere the transmission efficiency is sufficiently high, or in the casewhere the transmission efficiency is sufficiently improved by only theimpedance matching of the power supply apparatus, and the like, theimpedance matching circuit 454 may not be disposed.

The rectification circuit 455 rectifies the AC power supplied from thepower supply apparatus 100 to generate a direct current power. Therectification circuit 455 supplies the generated direct current power tothe charge control section 480 through the voltage stabilization circuit456 and the load connection circuit 457. The voltage stabilizationcircuit 456 performs control in order to keep the voltage of the directcurrent power constant.

In this regard, the power after the rectification by the rectificationcircuit 455 is directly supplied to the voltage stabilization circuit456. However, the configuration is not limited to this. For example, aconfiguration of disposing a smoothing circuit for smoothing the powerafter the rectification between the rectification circuit 455 and thevoltage stabilization circuit 456 may be employed.

The load connection circuit 457 performs control so that the apparatusgoes either to a load connected state or a load disconnected state underthe control of the power reception control circuit 453. Specifically, ifinstructed to disconnect a load, the load connection circuit 457 opensthe circuit between the rectification circuit 455 and the charge controlsection 480 in order to stop supplying direct current power. On theother hand, if instructed to connect a load, the load connection circuit457 closes the circuit between the rectification circuit 455 and thecharge control section 480.

The charge control section 480 controls the voltage and the current ofthe direct current power in order to charge the secondary battery 481.Also, the charge control section 480 supplies part of the charging powerto the load circuit 482 while charging the secondary battery 481. Thesecondary battery 481 stores the power charged by the charge controlsection 480. For example, a lithium ion battery, or the like is used asthe secondary battery 481. The load circuit 482 is a circuit thatoperates using power from the secondary battery 481 or the chargecontrol section 480.

In this regard, the charge control section 480 is disposed outside thepower reception control section 450. However, the charge control section480 may be included in the power reception control section 450. Thereby,the power reception control section 450 effectively restrict or stopsupplying power to the secondary battery 481 and the load circuit 482.In that case, the charge control section 480 may be included in thepower reception control circuit 453. On the other hand, the chargecontrol section 480 may be allowed to control at least part of the powerreception control section 450 while disposing the charge control section480 outside the power reception control section 450.

Also, the foreign object detection apparatus is disposed at the powerreception side. However, the foreign object detection apparatus may bedisposed at the power supply side in place of the power reception side.In this case, the detection coil 410 is disposed in the vicinity of thepower supply coil 160, and the foreign object detection section 460detects a foreign object in a magnetic field generated by the powersupply coil 160. Also, the foreign object detection apparatus isdisposed inside or outside the power supply apparatus 100. Also, theforeign object detection apparatus may be disposed on both the powersupply side and the power reception side.

Also, the power supply apparatus 100, and the power reception apparatus400 may further include a circuit, and the like in addition to theconfiguration exemplified in FIG. 2 and FIG. 3. For example, at leastone of the power supply apparatus 100, and the power reception apparatus400 may further include a display section for displaying a foreignobject detection result, and the like, a communication section forperforming bi-directional communication, a detection section fordetecting whether the power reception apparatus 400 has been placed onthe power supply apparatus 100, and the like.

FIGS. 4A and 4B are diagrams illustrating an example of the powerreception coil 430 and the detection coil 410 according to the firstembodiment. FIG. 4A is an example of a plan view of the power receptioncoil 430, and the detection coil 410.

The area of the coil face of the detection coil 410 is smaller than thatof the power reception coil 430. Also, the detection coil 410 isdisposed inside the power reception coil 430. Also, it is desirable forthe detection coil 410 to be disposed such that the center thereofsubstantially matches the center of the power reception coil 430.

FIG. 4B is an example of sectional views taken along line IVB-IVB of thepower reception coil 430, and the detection coil 410 of FIG. 4A. Asillustrated in FIG. 4B, in order to make the apparatus thin, and fromthe viewpoint of implementation and mass production, it is desirable todispose the detection coil 410, and the power reception coil 430 on thesubstantially same plane.

In this regard, in FIG. 4B, the detection coil 410, and the powerreception coil 430 are disposed substantially on the same plane, but maybe disposed on different planes.

The power reception coil 430, the detection coil 410, and the powersupply coil 160 are formed by winding a conductive wire, for example,and the winding number is any. In this regard, these coils may be formedby any way other than winding a conductive wire. For example, thesecoils may be formed by a conductive pattern, such as a printed circuitboard, a flexible printed circuit board, and the like. These coils arereferred to as pattern coils or pattern loops. It is also possible toform a pattern coil by printing or depositing a conductive material on asubstrate, or fabricating a conductive metal plate or sheet, and thelike.

Also, these coils may be formed by winding a wire produced by bundling aplurality of conductive strands. Specifically, these coils are formed bywinding a wire produced by bundling two conductive strands, a wireproduced by bundling three conductive strands, and the like. The formeris called a bifilar wound coil, and the latter is called a trifilarwound coil. Also, the wound wire of each coil may be a wire produced bytwisting a plurality of conductive strands (that is to say, a litzwire).

Also, for these coils, a spiral shaped coil or a helical shaped coil inwhich a wire is wound in a thickness direction may be used. Also, eachcoil may be formed in an α-winding shape in which a spiral shaped coilis folded back by two layers, in a more multi-layered spiral shape, andso on.

Also, in order to prevent magnetic flux leakage, and to improvetransmission efficiency, a shield made of a magnetic body, a magnet, anelectric conductor, metal, or the like may be disposed.

Also, the detection coil 410 may be disposed inside the part where thewire of the power reception coil 430 is wound (that is to say, a track).Further, a coil for use other than non-contact power supply, such as aninduction heating coil, a wireless communication coil, and the like maybe used for the detection coil 410 in combination. In addition, thepower reception coil 430 and the detection coil 410 may be used incombination depending on the configuration of the non-contact powersupply system. In this regard, in addition to the cases of using thesame coil in combination, it is assumed that there are cases where apart of a coil is used in combination using switching, and the like.

If there is a conductive foreign object, such as a metal, or the like ina magnetic field formed by the power supply apparatus 100, an eddycurrent occurs in the foreign object by magnetic induction effect. Theforeign object is heated by the Joule heat caused by the eddy current.Also, the magnetic field generated by the eddy current works on thedetection coil 410 and the power reception coil 430, and changes theelectric characteristic, such as the impedance of the equivalent circuitthereof, or the like.

In particular, if there is a foreign object in the vicinity of the wireof the power reception coil 430, the magnetic field generated by theforeign object disperses the magnetic field in the vicinity of the wire,and thus the impedance of the equivalent circuit of the power receptioncoil 430 increases. On the other hand, if there is a foreign object nearthe center of the power reception coil 430, by a similar principle ofinserting an iron core in the center of the power reception coil 430,the magnetic field concentrates near the center, and thus the impedanceof the power reception coil 430 decreases. Accordingly, it is possiblefor the power reception apparatus 400 to detect a foreign object fromvariations of the impedance using the impedance when there is no foreignobject as a reference value.

Example of Configuration of Foreign Object Detection Section

FIG. 5 is a block diagram illustrating an example of a configuration ofthe foreign object detection section 460 according to the firstembodiment. The foreign object detection section 460 includes a signalprocessing section 461, a measurement value holding section 462, anelectric characteristic acquisition section 463, and a comparisonsection 464.

The signal processing section 461 performs predetermined signalprocessing on a measurement value. Specifically, separation of a realcomponent and an imaginary component of the AC signal is performed asthe signal processing. The signal processing section 461 causes themeasurement value holding section 462 to hold the power reception coilcurrent I_(2off) when measured at load disconnection time. Also, thesignal processing section 461 causes the measurement value holdingsection 462 to hold individual real components of the power receptioncoil voltage V_(2off), and the detection coil voltage V_(3off) when aload is disconnected. After the individual measurement values at loaddisconnected time are held, the signal processing section 461 generatesa measurement termination notification, and supplies the measurementtermination notification to the power reception control circuit 453.

And when a load is connected, the signal processing section 461 causesthe measurement value holding section 462 to hold a power reception coilcurrent I_(2on) measured at that time. Also, the signal processingsection 461 causes the measurement value holding section 462 to hold thereal components of the power reception coil voltage V_(2on), and thedetection coil voltage V_(3on) that were measured when a load isconnected. The measurement value holding section 462 holds themeasurement values.

In this regard, the signal processing section 461 may further performprocessing for separating a fundamental wave component from higherharmonic wave components and noise component to extract only thefundamental component as signal processing. Also, the signal processingsection 461 may further perform processing for obtaining information onthe carrier frequency, and information on the duty ratio of the carrierwave, and notifying the information to the power reception controlcircuit 453, and the like. Also, in the case of a configuration in whichthe measurement section 451 measures a DC voltage, and the like, it isnot necessary for the signal processing section 461 to separate the realcomponent and the imaginary component.

The electric characteristic acquisition section 463 obtains parametersindicating an electric characteristic of at least one of the powerreception coil 430 and the detection coil 410 from the measurementvalues. The electric characteristic acquisition section 463 obtains theimpedance of the power reception coil 430 of an equivalent circuit as aparameter, for example. Specifically, the electric characteristicacquisition section 463 reads power reception coil currents I_(2on) andI_(2off), power reception coil voltages V_(2on) and V_(2off), anddetection coil voltages V_(3on) and V_(3off) from the measurement valueholding section 462. And the electric characteristic acquisition section463 obtains a resistor R2 as impedance of the power reception coil 430from those measurement values using the following expressions 1 to 4.The electric characteristic acquisition section 463 supplies theobtained resistor R2 to the comparison section 464.

$\begin{matrix}{R_{2} \approx \frac{\Delta\; K}{{I_{2{on}}/{{real}( V_{3{on}} )}} - {I_{2{off}}/{{real}( V_{3{off}} )}}}} & \lbrack {{Expression}\mspace{14mu} 1} \rbrack \\{{\Delta\; K} = {K_{off} - K_{on}}} & \lbrack {{Expression}\mspace{14mu} 2} \rbrack \\{K_{off} = \frac{{real}( V_{2{off}} )}{{real}( V_{3{off}} )}} & \lbrack {{Expression}\mspace{14mu} 3} \rbrack \\{K_{on} = \frac{{real}( V_{2{on}} )}{{real}( V_{3{on}} )}} & \lbrack {{Expression}\mspace{14mu} 4} \rbrack\end{matrix}$

Here, Expression 1 is derived from (R₂+R_(on))×I_(2on)≅real (V_(2on))and (R₂+R_(off))×I_(2off)≅real(V_(2off)). In these expressions, R_(on)is a real part of the impedance of the circuit that is substantiallyconnected to the power reception coil 430 when a load is connected, andR_(off) is a real part of the impedance of the circuit load that issubstantially connected to the power reception coil 430 when a load isdisconnected. Also, in Expression 1, Expression 3, and Expression 4,real(A) is a function that returns a real component of A.

In this regard, in Expression 3 and Expression 4, a ratio of the realcomponents is obtained. However, a ratio of the imaginary components ora ratio of the absolute values may be obtained in place of the realcomponents.

Also, the electric characteristic acquisition section 463 obtains theresistor R₂ as the impedance of the power reception coil 430. However,the reactance of the power reception coil 430 may be obtained in placeof the resistor.

The comparison section 464 compares the parameter obtained by theelectric characteristic acquisition section 463 with an upper limitthreshold value, and a lower limit threshold value. Here, the upperlimit threshold value is set to a higher value than the reference valueusing a parameter value when there is no foreign object as a referencevalue. Also, the lower limit threshold value is set to a lower valuethan the reference value. If the parameter is higher than the upperlimit threshold value, or the parameter is lower than the lower limitthreshold value, the comparison section 464 detects a foreign object.The comparison section 464 supplies the detection result of the foreignobject to the power reception control circuit 453.

In this regard, the foreign object detection section 460 obtainsindividual measurement values of the amount of power supply when a loadis connected, and the amount of power supply when a load isdisconnected. However, the present disclosure is not limited to thisconfiguration. For example, two different amounts of power may besupplied in sequence while the power reception apparatus 400 isconnected to a load, or disconnected to a load, and the foreign objectdetection section 460 may obtain measurement values in sequence at thetime of those amounts of power supply. In this case, the load connectioncircuit 457 is not necessary for the power reception apparatus 400 forthe measurement. However, it is desirable to dispose the load connectioncircuit 457 in the power reception apparatus 400 from the viewpoint ofoperation and safety.

Operation Example of Power Supply Apparatus

FIG. 6 is a flowchart illustrating an example of operation of the powersupply apparatus 100 according to the first embodiment. This operationis started when an external power source is turned on to the powersupply apparatus 100, for example. The power supply apparatus 100supplies a minimum amount of power W1 through a magnetic field (stepS901).

And the power supply apparatus 100 determines whether an increase in theamount of power supply has been requested or not by the power supplycontrol signal (step S902). If an increase in the amount of power supplyhas not been requested (step S902: No), the processing of the powersupply apparatus 100 returns to step S902.

If an increase in the amount of power supply has been requested (stepS902: Yes), the power supply apparatus 100 increases the amount of powersupply to W2 (step S903). And the power supply apparatus 100 determineswhether a decrease in the amount of power supply has been requested ornot by the power supply control signal (step S904). If a decrease in theamount of power supply has not been requested (step S904: No), theprocessing of the power supply apparatus 100 returns to step S904.

If a decrease in the amount of power supply has been requested (stepS904: Yes), the power supply apparatus 100 decreases the amount of powersupply to W1 (step S905), and the processing returns to step S902.

Operation Example of Power Reception Apparatus

FIG. 7 is a flowchart illustrating an example of operation of the powerreception apparatus 400 according to the first embodiment. Thisoperation is started when power is supplied from the power supplyapparatus 100, for example. The power reception apparatus 400 goes to aload disconnected state by the connection control signal (step S951).The power reception apparatus 400 measures the power reception coilcurrent I_(2off), the power reception coil voltage V_(2off), and thedetection coil voltage V_(3off) (step S952).

And the power reception apparatus 400 goes to a load-connected state bythe connection control signal to increase the amount of power supply bythe power supply control signal (step S953). The power receptionapparatus 400 measures the power reception coil current I_(2on), thepower reception coil voltage V_(2on), and the detection coil voltageV_(3on) (step S954). The power reception apparatus 400 obtains theparameter of the electric characteristic from the measurement valuesusing Expression 1, and the like (step S956). The power receptionapparatus 400 determines whether the parameter is higher than the upperlimit threshold value or not (step S957).

If the parameter is not higher than the upper limit threshold value(step S957: No), the power reception apparatus 400 determines whetherthe parameter is lower than the lower limit threshold value (step S958).If the parameter is higher than the upper limit threshold value (stepS957: Yes), or the parameter is lower than the lower limit thresholdvalue (step S958: Yes), the power reception apparatus 400 detects aforeign object (step S959). And the power reception apparatus 400decreases the amount of power supply by the power supply control signal(step S960). If the parameter is higher than the lower limit thresholdvalue (step S958: No), or after step S960, the power reception apparatus400 terminates the operation for detecting a foreign object.

In this regard, the power reception apparatus 400 performs the detectionprocessing illustrated in FIG. 7 only once at power reception time.However, this detection processing may be performed on a regular basis.

FIG. 8 is a graph illustrating an example of temperature change of aforeign object according to the first embodiment. The vertical axis inFIG. 8 represents temperature of a metallic foreign object generatedheat by lines of magnetic force from the power supply apparatus 100. Thehorizontal axis represents the amount of difference between the centerof the foreign object and the center of the power reception coil 430.The unit of temperature is ° C., for example. The unit of the amount ofdifference is millimeter (mm). It is assumed that the wire of the powerreception coil 430 is disposed at a position within approximately −13 mmfrom the center of the power reception coil 430. The temperature of theforeign object increases as the amount of difference goes from −30 mm tocome close to 0 mm, and becomes highest at a distance of about −13 mm.Also, the temperature is lower than the peak in the case where theamount of difference is 0 mm, but becomes a temperature higher than thatat −30 mm. Accordingly, it is understood that when there is a foreignobject inside the power reception coil 430, the temperature of theforeign object becomes relatively high. Thus, for example, the powerreception apparatus 400 is designed such that a permissible value of atemperature at which the power reception apparatus 400 is not damaged isdetermined, and a range that is higher than the temperature and in whichthe foreign object generates heat (from −20 mm to 0 mm, or the like) isassumed to be a range of detecting a foreign object in order to detect aforeign object in the detection range.

FIG. 9 is a graph illustrating an example of impedance change of thepower reception coil 430 according to the first embodiment. The verticalaxis in FIG. 9 represents impedance of the power reception coil 430, andthe horizontal axis represents the amount of difference between thecenter of a foreign object and the center of the power reception coil430. In FIG. 9, it is assumed that the measuring conditions, such as thesize and the material of the foreign object, the amount of power supply,and the like are the same as those of FIG. 8.

As illustrated in FIG. 9, the impedance of the power reception coil 430becomes higher than the reference value in the vicinity of the track ofthe power reception coil, and becomes lower than the reference value inthe vicinity of the center. Accordingly, by setting an upper limitthreshold value Th_UR2, which is higher than the reference value, and alower limit threshold value Th_LR2, which is lower than the referencevalue, to suitable values, it is possible for the power receptionapparatus 400 to correctly detect a foreign object in the vicinity ofthe track at which the foreign object generates heat at a temperaturehigher than the permissible value, or in the vicinity of the center.

In this manner, by the first embodiment of the present technique, thepower reception apparatus detects a foreign object in the case where theimpedance is lower than the lower limit threshold value, and thus isallowed to detect the foreign object in the vicinity of the center ofthe power reception coil 430 with high precision. Also, the powerreception apparatus detects a foreign object in the case where theimpedance is higher than the upper limit threshold value, and thus isallowed to detect the foreign object in the vicinity of the track of thepower reception coil 430 with high precision.

2. Second Embodiment

In the first embodiment, the power reception apparatus 400 detects aforeign object from the impedance of the power reception coil 430.However, it is possible to detect a foreign object from ΔK. The powerreception apparatus 400 according to the second embodiment is differentfrom the first embodiment in the point that a foreign object is detectedfrom ΔK.

The measurement section 451 according to the second embodiment does notmeasure the power reception coil current I₂. Accordingly, in themeasurement section 451, an ammeter, or the like becomes unnecessary.

Also, the foreign object detection section 460 according to the secondembodiment obtains ΔK using Expression 2 to Expression 4, and detects aforeign object by comparing ΔK thereof and the threshold value.

FIG. 10 is a graph illustrating an example of change of ΔK according tothe second embodiment. The vertical axis in FIG. 10 represents ΔK, andthe horizontal axis represents the amount of difference between thecenter of the foreign object and the center of the power reception coil430. In FIG. 10, it is assumed that the measuring conditions, such asthe size and the material of the foreign object, the amount of powersupply, and the like are the same as those of FIG. 8.

As illustrated in FIG. 10, ΔK of the power reception coil 430 becomeshigher than the reference value in the vicinity of the track of thepower reception coil, and becomes lower than the reference value in thevicinity of the center. Accordingly, by setting an upper limit thresholdvalue Th_UΔK, which is higher than the reference value, and a lowerlimit threshold value Th_LΔK, which is lower than the reference value tosuitable values, it is possible for the power reception apparatus 400 tocorrectly detect a foreign object in the vicinity of the track at whichthe foreign object generates heat at a temperature higher than thepermissible value, or in the vicinity of the center.

In this manner, by the second embodiment, it is possible to correctlydetect a foreign object on the basis of ΔK.

3. Third Embodiment

In the first embodiment, the power reception apparatus 400 detects aforeign object from the impedance of the power reception coil 430.However, it is possible to detect a foreign object from a voltage ratiobetween the power reception coil 430 and the detection coil 410. Thepower reception apparatus 400 according to the third embodiment isdifferent from the first embodiment in the point that a foreign objectis detected the voltage ratio.

The measurement section 451 according to the third embodiment does notmeasure the power reception coil current I₂. Accordingly, in themeasurement section 451, an ammeter, or the like becomes unnecessary.Also, the measurement section 451 does not measure the power receptioncoil voltage V_(2off) and the detection coil voltage V_(3off) when aload is disconnected. These measurements become unnecessary, and thusthe latency from a measurement start of the measurement value to adetection end of a foreign object becomes short.

Also, the foreign object detection section 460 according to the thirdembodiment obtains the voltage ratio using Expression 4, and detects aforeign object by comparing the voltage ratio and the threshold value.

FIG. 11 is a graph illustrating an example of change of the voltageratio according to the third embodiment. The vertical axis in FIG. 11represents the voltage ratio obtained from Expression 4. The horizontalaxis represents the amount of difference between the center of a foreignobject and the center of the power reception coil 430. In FIG. 11, it isassumed that the measuring conditions, such as the size and the materialof the foreign object, the amount of power supply, and the like are thesame as those of FIG. 8.

As illustrated in FIG. 11, the voltage ratio of the power reception coil430 becomes higher than the reference value in the vicinity of the trackof the power reception coil, and becomes lower than the reference valuein the vicinity of the center. Accordingly, by setting an upper limitthreshold value Th_UR, which is higher than the reference value, and alower limit threshold value Th_LR, which is lower than the referencevalue to suitable values, it is possible for the power receptionapparatus 400 to correctly detect a foreign object in the vicinity ofthe track at which the foreign object generates heat at a temperaturehigher than the permissible value, or in the vicinity of the center.

In this manner, by the third embodiment, it is possible to correctlydetect a foreign object on the basis of the voltage ratio.

4. Fourth Embodiment

In the first embodiment, the power reception apparatus 400 detects aforeign object from the impedance of the power reception coil 430.However, it is possible to detect a foreign object from a detection coilvoltage. The power reception apparatus 400 according to the fourthembodiment is different from the first embodiment in the point that aforeign object is detected by the detection coil voltage V_(3on).

The measurement section 451 according to the fourth embodiment measuresonly the detection coil voltage V_(3on). Also, the voltage and thecurrent of the power reception coil ought not to be measured, and thusthe configuration of the measurement section 451 becomes simple.

Also, the foreign object detection section 460 according to the fourthembodiment compares the real component of the detection coil voltageV_(3on) and the threshold value in order to detect a foreign object.

In this regard, the foreign object detection section 460 detects aforeign object by the real component of the detection coil voltageV_(3on). However, the present technique is not limited to thisconfiguration. For example, the foreign object detection section 460 maydetect a foreign object by the imaginary component of the detection coilvoltage V_(3on) or the absolute value of the detection coil voltageV_(3on).

FIG. 12 is a graph illustrating an example of change of the detectioncoil voltage V_(3on) according to the fourth embodiment. The verticalaxis in FIG. 12 represents the real component of the detection coilvoltage V_(3on), and the horizontal axis represents the amount ofdifference between the center of a foreign object and the center of thepower reception coil 430. In FIG. 12, it is assumed that the measuringconditions, such as the size and the material of the foreign object, theamount of power supply, and the like are the same as those of FIG. 8.

As illustrated in FIG. 12, the detection coil voltage V_(3on) of thepower reception coil 430 becomes higher than the reference value in thevicinity of the track of the power reception coil, and becomes lowerthan the reference value in the vicinity of the center. Accordingly, bysetting an upper limit threshold value Th_UV3, which is higher than thereference value, and a lower limit threshold value Th_LV3, which islower than the reference value to suitable values, it is possible forthe power reception apparatus 400 to correctly detect a foreign objectin the vicinity of the track at which the foreign object generates heatat a temperature higher than the permissible value, or in the vicinityof the center.

In this manner, by the fourth embodiment, it is possible to correctlydetect a foreign object on the basis of the detection coil voltage.

Variations

In the first embodiment, the detection coil 410 is disposed with thelayout exemplified in FIGS. 4A and 4B. However, the detection coil 410may be disposed with a layout different from that in FIGS. 4A and 4B.The power reception apparatus 400 according to a variation is differentfrom the first embodiment in the point that the disposition of thedetection coil 410 is different from that in FIGS. 4A and 4B.

FIGS. 13A to 13G are sectional views illustrating examples ofdisposition of a power reception coil and a detection coil according tovariations, respectively.

FIG. 13A is an example in which a part of wire of the detection coil 410is provided with a gap. In FIG. 13B, the number of turns of thedetection coil 410 is decreased from that in FIG. 13A.

FIG. 13C is an example in which the outermost edge of the detection coil410 is disposed on the track of the power reception coil 430.

FIG. 13D is an example in which the center of the detection coil 410 isshifted from the center of the power reception coil 430 such that one ofboth ends of the detection coil 410 is disposed on the track of thepower reception coil 430, and the other end is disposed outside thepower reception coil 430.

FIG. 13E is an example in which the center of the detection coil 410 ispositioned over the track of the power reception coil 430.

FIG. 13F is an example in which the center of the detection coil 410 isshifted from the center of the power reception coil 430 such that one ofboth ends of the detection coil 410 is disposed on the track of thepower reception coil 430, and the other end is disposed inside the powerreception coil 430.

FIG. 13G is an example in which the center of the detection coil 410 isshifted from the center of the power reception coil 430 in a range wherethe detection coil 410 is positioned inside the power reception coil430.

In this regard, the above-described embodiments are examples ofrealizing the present technique. There are corresponding relationshipsbetween the matters in the embodiments and the matters specifying thedisclosure in the claims, respectively. In the same manner, there arecorresponding relationships between the matters specifying thedisclosure in the claims and the matters having the same names in theembodiments of the present technique, respectively. However, the presenttechnique is not limited to the above-described embodiments. It ispossible to achieve the present technique by making various changes onthe embodiments without departing from the gist of the presenttechnique.

Also, the processing procedure described in the above embodiments may beunderstood as methods that include a series of the processing procedure.Also, the processing procedure may be understood as a program thatcauses a computer to perform the series of the processing procedure or arecording medium for storing the program. It is possible to use, as therecording medium, a CD (Compact Disc), an MD (MiniDisc), a DVD (DigitalVersatile Disc), a memory card, a Blu-ray (registered trademark) disc,and the like, for example.

In this regard, it is also possible to configure the present techniqueas follows.

(1) A detection apparatus including:

a measurement coil disposed in a vicinity of a power reception coilconfigured to receive power supplied through a magnetic field;

a measurement section configured to measure a voltage of the measurementcoil as a measurement coil voltage; and

a foreign object detection section configured to obtain an electricalcharacteristic value of at least one of the power reception coil and themeasurement coil on the basis of the measurement coil voltage, and todetect a foreign object in the magnetic field if the electricalcharacteristic value is lower than a predetermined lower limit thresholdvalue.

(2) The detection apparatus according to (1),

wherein if the electrical characteristic value is lower than the lowerlimit threshold value, or if the electrical characteristic value ishigher than an upper limit threshold value greater than the lower limitthreshold value, the foreign object detection section is configured todetect the foreign object.

(3) The detection apparatus according to (2),

wherein the upper limit threshold value is higher than a reference valuebeing the electrical characteristic value when there is no foreignobject, and the lower limit threshold value is a lower value than thereference value.

(4) The detection apparatus according to (1) or (2),

wherein the measurement section is configured to further measure avoltage and a current of the power reception coil, and

the foreign object detection section is configured to obtain impedanceof the power reception coil from the measurement coil voltage, and thevoltage and the current of the power reception coil as the electricalcharacteristic value.

(5) The detection apparatus according to any one of (1) to (4),

wherein the measurement section is configured to further measure avoltage of the power reception coil as a power reception coil voltage,and

the foreign object detection section is configured to obtain a voltageratio of the measurement coil voltage and the power reception coilvoltage as the electrical characteristic value.

(6) The detection apparatus according to any one of (1) to (5),

wherein the measurement section is configured to further measure avoltage of the power reception coil as a power reception coil voltage,

the power reception coil is configured to receive first and second powerhaving a different amount of power with each other in sequence, and

the foreign object detection section is configured to obtain, as theelectrical characteristic, a difference between the voltage ratioobtained when the first power is received, and the voltage ratioobtained when the second power is received.

(7) The detection apparatus according to any one of (1) to (6),

wherein the measurement coil is configured to have a smaller coilsurface area than that of the power reception coil.

(8) The detection apparatus according to (7),

wherein the measurement coil is disposed inside the power receptioncoil.

(9) The detection apparatus according to any one of (1) to (8),

wherein the measurement coil is disposed on a substantially same planeas that of the power reception coil.

(10) The detection apparatus according to any one of (1) to (9),

wherein the measurement coil is disposed at a position where a coilsurface of the measurement coil and that of the power reception coilhave a substantially same center position.

(11) The detection apparatus according to any one of (1) to (10),

wherein the power is power supplied from a power supply apparatus, and

the detection apparatus further including a transmission sectionconfigured to transmit a control signal requesting a decrease in anamount of the power if the foreign object is detected.

(12) A detection apparatus including:

a measurement coil disposed in a vicinity of a power supply coilconfigured to supply power through a magnetic field;

a measurement section configured to measure a voltage of the measurementcoil as a measurement coil voltage; and

a foreign object detection section configured to obtain an electricalcharacteristic value of at least one of the power reception coil and themeasurement coil on the basis of the measurement coil voltage, and todetect a foreign object in the magnetic field if the electricalcharacteristic value is lower than a predetermined lower limit thresholdvalue.

(13) A power supply system including:

a power supply coil configured to supply power through a magnetic field;

a power reception coil configured to receive the power;

a measurement coil disposed in a vicinity of the power reception coil;

a measurement section configured to measure a voltage of the measurementcoil as a measurement coil voltage; and

a foreign object detection section configured to obtain an electricalcharacteristic value of at least one of the power reception coil and themeasurement coil on the basis of the measurement coil voltage, and todetect a foreign object in the magnetic field if the electricalcharacteristic value is lower than a predetermined lower limit thresholdvalue.

(14) A method of controlling a detection apparatus, the methodincluding:

measuring by a measurement section, as a measurement coil voltage, avoltage of a measurement coil disposed in a vicinity of a powerreception coil configured to receive power supplied through a magneticfield; and

detecting a foreign object by a foreign object detection sectionobtaining an electrical characteristic value of at least one of thepower reception coil and the measurement coil on the basis of themeasurement coil voltage, and detecting the foreign object in themagnetic field if the electrical characteristic value is lower than apredetermined lower limit threshold value.

What is claimed is:
 1. A power supply device comprising: a power supplycontrol section configured to control an amount of power wirelesslysupplied from a power supply coil to a power reception coil of a powerreception apparatus through a magnetic field; a measurement sectionconfigured to measure a power supply coil voltage of the power supplycoil; and a foreign object detection section configured to obtain anelectrical characteristic value of the power supply coil based on thepower supply coil voltage, and detect a presence or an absence of aforeign object in the magnetic field based on the electricalcharacteristic value and a predetermined threshold value, wherein afirst amount of power is supplied from the power supply coil to thepower reception coil when the measurement section measures the powersupply coil voltage, and wherein a second amount of power is suppliedfrom the power supply coil to the power reception coil when the foreignobject detection section detects the absence of the foreign object inthe magnetic field, the second amount of power is higher than the firstamount of power.
 2. The power supply device according to claim 1,wherein the foreign object detection section is further configured toset the predetermined threshold value based on a reference value that isthe electrical characteristic value indicating the absence of theforeign object in the magnetic field.
 3. The power supply deviceaccording to claim 2, wherein the predetermined threshold value is lowerthan the reference value.
 4. The power supply device according to claim1, wherein the measurement section is further configured to measure apotential difference between two ends of the power supply coil as thepower supply coil voltage.
 5. The power supply device according to claim1, wherein the foreign object detection section is configured to detectthe foreign object in the magnetic field when the electricalcharacteristic value is lower than the predetermined threshold value. 6.The power supply device according to claim 1, wherein the power supplycontrol section is further configured to control the amount of power tothe power reception coil in accordance with a power supply controlsignal wirelessly received from the power reception apparatus.
 7. Apower supply apparatus comprising: a power supply face having a certainarea, a surface of the power supply face is configured to be placed apower reception apparatus; a resonance circuit including a capacitor anda power supply coil, the power supply coil is arranged to a lower partor the surface of the power supply face; a power supply control sectionconfigured to control an amount of power wirelessly supplied from thepower supply coil to a power reception coil of the power receptionapparatus through a magnetic field; a measurement section configured tomeasure a power supply coil voltage of the power supply coil; and aforeign object detection section configured to obtain an electricalcharacteristic value of the power supply coil based on the power supplycoil voltage, and detect a presence or an absence of a foreign object inthe magnetic field based on the electrical characteristic value and apredetermined threshold value, wherein a first amount of power issupplied from the power supply coil to the power reception coil when themeasurement section measures the power supply coil voltage, and whereina second amount of power is supplied from the power supply coil to thepower reception coil when the foreign object detection section detectsthe absence of the foreign object in the magnetic field, the secondamount of power is higher than the first amount of power.
 8. The powersupply apparatus according to claim 7, wherein the foreign objectdetection section is configured to detect the foreign object in themagnetic field when the electrical characteristic value is lower thanthe predetermined threshold value.
 9. The power supply apparatusaccording to claim 7, wherein the foreign object detection section isfurther configured to set the predetermined threshold value based on areference value that is the electrical characteristic value indicatingthe absence of the foreign object in the magnetic field.
 10. The powersupply apparatus according to claim 9, wherein the predeterminedthreshold value is lower than the reference value.
 11. The power supplyapparatus according to claim 7, wherein the measurement section isfurther configured to measure a potential difference between two ends ofthe power supply coil as the power supply coil voltage.
 12. The powersupply apparatus according to claim 7, wherein the power supply controlsection is further configured to control the amount of power to thepower reception coil in accordance with a power supply control signalwirelessly received from the power reception apparatus.